Stabilization of thermally unstable liquid hydrocarbon fuels



United States Patent 3,222,145 STABELIZATION OF THERMALLY UNSTABLE LIQUID HYDROCARBON FUELS George Belo, Franklin Township, Allegheny County, and Arthur V. Churchill, Oaltmont, Pa., assignors to Gulf Research 8; Development Company, Pittsburgh, Pa, a corporation of Delaware No Drawing. Filed Dec. 28, 1960, Ser. No. 78,854

20 Claims. (Cl. 44--66) This invention relates to improving the thermal stability of combustion gas turbine fuels. More particularly, the invention relates to reducing the tendency of combustion gas turbine fuels to form solid deposits at very high service temperatures by incorporating therein small amounts of a monoester of a higher fatty acid and a polyglycerol.

Combustion gas turbine fuel is presently employed as a cooling medium, or heat sink, in combustion gas turbine powered aircraft to remove heat by indirect heat exchange from lubricating oil that has absorbed heat developed in the engine by the compression of combustion air, by fuel combustion, and by friction of moving parts. As a result, the fuel is subjected to heat transfer surface temperatures during service of the order of 300 to 400 F. for relatively substantial time intervals. In addition, the fuel is subjected to even higher temperatures, of the order of 500 F., for short periods of time in the area of the nozzles or orifices from which the fuel is introduced into the combustion chamber of the engine. As a result, certain components of the fuel tend to undergo decomposition due to polymerization, oxidation, and thermal decomposition, and to form solid or semi-solid degradation products that clog the fuel orifices and thereby interfere with proper combustion of the fuel. Ordinary stabilizing agents, anti-oxidants and the like, of the kind that are employed to stabilize the fuels during storage have been found inadequate to inhibit deterioration of the fuels at the high service temperatures encountered in aviation turbine engines.

The present invention relates to improving the thermal stability of liquid hydrocarbon combustion gas turbine fuels, such as aviation turbine fuels, and to reducing the tendencies of such fuels to form deposits on heat transfer surfaces at temperatures in excess of 300 F. and in the fuel inlet regions of the combustion zones of the engines in which the fuels are consumed, whereby such fuels are rendered more suitable for use in such engines. It has been found that the thermal stability characteristics of the above-indicated fuels, as well as other characteristics of these and other hydrocarbon oils, can be improved by incorporating therein a small amount of a monoester of a fatty acid that contains 8 to 18 carbon atoms and a polyglycerol that has an average molecular weight of about 166 to 462. In a preferred embodiment the monoester is the ester of oleic acid and mixed polyglycerols having an average of four CH CHOHCH O units per molecule, but monoesters of other fatty acids including saturated acids such as Oxo-octanoic, lauric, palmitic, stearic, linoleic, and linolenic acids and other polyglycerols can be used. When still greater protection is desired against clogging of fuel orifices by thermal degradation of thermally unstable fuel contacted by the hot fuel orifices under high service temperatures than is provided by the polyglycerol monoesters alone, without sacrificing the already exceptional protection against fouling of heat transfer surfaces provided by the polyglycerol monoesters alone, there can also be included in the fuel compositions of this invention a compatible supplemental anticlogging agent, such as (I) an oil-soluble nitrogenous anticlogging copolymer containing as its essential monomeric components, in a weight ratio of about 0.03 to 1:1, preferably 0.05 to 0.75:1, of (a) a copolymerizable alkyl ester of an acid such as acrylic and alkacrylic acids whose alkyl ester substituent contains 8 to 18 carbon atoms, and (b) a copolymerizable unsaturated compound containing one ethylenic linkage copolymerizable with the aforesaid alkyl ester and a nitrogen-containing substituent group that is not polymerizable with said alkyl ester, or (II) an oilsoluble phosphosulfurized hydrocarbon product obtained by reacting a phosphorus sulfide with an aliphatic hydrocarbon. A specific example of a preferred copolymer is the 1:9 weight ratio copolymer of di(Oxo-octyl)aminoethyl methacrylate and lauryl methacrylate, but other copolymers having their extralinear nitrogenous substituents linked to the polymer chain through a linkage other than an ester linkage, for example, a quaternary ammonium salt linkage or an amine addition salt linkage, including the dehydrated or amido form of such addition salt linkage, can be used. Specific examples of such other copolymers include the 1:9 weight ratio copolymer of soya a'lkyltrimethylammonium methacrylate and lauryl methacrylate and the 1:9 Weight ratio copolymer of di(Oxooctyl)amonium methacrylate and lauryl methacrylate. A specific example of an oil-soluble phosphosulfurized aliphatic hydrocarbon is the phosphosulfurized product Obtained by reacting P 8 with pentapropylene, but phosphosulfurized products obtained by reacting other phosphorus sulfides and other aliphatic hydrocarbons, including other olefin polymers, can be used. The polyglycerol monoesters are effective as such or in combination with the supplemental anticlogging agents disclosed herein when employed in small amounts. Proportions in the range of 10 to 20 pounds per 1,000 barrels of fuel are preferred, but other proportions, for example, about 2.5 to 50 pounds or more per thousand barrels of fuel, can be used. When the supplemental anticlogging agents are employed in conjunction with the polyglycerol monoesters disclosed herein, the respective materials can be used in varying proportions with respect to each other. The respective materials are preferably added to the fuels in about equal proportions by weight, but other proportions can be used provided the compound present in the smaller amount is present in an amount corresponding to at least about 2.5 pounds per thousand barrels of fuel. Ordinarily, the respective materials will be employed in weight ratios in the range of about 1:4 to 4:1, but other weight ratios, for example, 1:10 to 10:1 can be used.

The exact manner in which the polyglycerol monoesters disclosed herein function to improve the thermal stability of combustion gas turbine fuels has not been definitely determined. Nevertheless, inasmuch as the polyglycerol monoesters disclosed herein eifect a reduction in heat transfer surface deposits as well as in fuel nozzle deposits, notwithstanding the fact that the two kinds of deposits diifer chemically and physically from each other and notwithstanding that both types of deposits are not normally reduced by the same addition agent, it follows that the polygylcerol monoesters must function in at least two different ways.

In view of the distinct and different nature of heat transfer surface deposits and fuel nozzle deposits, it might be supposed that the polygylcerol monoesters disclosed herein and the supplemental anti-clogging agents, when the latter are employed, function independently of one another. However, this is contradicted by the fact that some materials that are effective as such to inhibit fuel nozzle deposits have been found to be ineffective to inhibit such deposits in the presence of polyglycerol monoesters. The fact that normally effective anticlogging agents are not necessarily effective to inhibit fuel nozzle deposits in the presence of the polyglycerol monoesters suggests strongly an interaction between the monoesters and the anti-clogging agents disclosed herein.

Although it has been stated that heat transfer surface deposits and fuel nozzle deposits differ markedly from each other, it should also be emphasized parenthetically that each of these types of deposits also differs respectively from deposits formed from fuels at relatively low temperatures, that is, below 300 F. The distinction between low or moderate temperature deposits and the high temperature deposits with which the present invention is concerned is emphasized by the fact that many of the distillate fuels that are benefited by the use of the improvement agents, disclosed herein form no deposits whatsoever at temperatures significantly below 300 F. and also by the fact that many improvement agents that are effective ot reduce deposits formed in hydrocarbon oils that are unstable at temperatures below about 300 F. have no effect whatsoever in reducing deposits formed in combustion gas turbine fuels at higher temperatures.

The polyglycerol monoesters disclosed herein can be prepared in any convenient manner, for example, by direct esterification of a selected fatty acid containing 8 to 18 carbon atoms and polyglycerol in a 1:1 mol ratio in the presence of a sodium hydroxide catalyst. The polyglycerols referred to herein are condensation products of glycerol containing 2 to 6 or more molecular units of glycerol. In the case of a preferred polyglycerol monoester, a polyglycerol mono-oleate marketed under the name Emcol 14, the polyglycerol is a condensation product or polymer averaging four molecules of glycerol per molecule of condensation product and is stated by the manufacturer to have the following structure:

where each of the unsatisfied valence bonds is attached to a hydrogen atom. Examples of other polylycerol monoesters the us of which is included by this invention are polyglycerol mono-Oxo-octanoate, polyglycerol monolaurate, polyglycerol mono-Oxo-tridecanoate, polyglycerol monopalmitate, polyglycerol monostearate, polyglycerol monolinoleate, and polyglycerol monolinolenate.

Any suitable anticlogging agent can be used to supplement the anticlogging properties of the polyglycerol monoesters disclosed herein. That is, any anticlogging agent can be used that will reduce deposition of thermal degradation fuel deposits in the fuel inlet area of a combustion gas turbine engine in the presence of the polyglycerol monoesters described herein without significantly detracting from the advantageous properties of such monoesters. As indicated, good results are obtainable with various chemical types of anticlogging agents, including oil-soluble nitrogen-containing copolymers and oil-soluble, phosphosulfurized hydrocarbons.

The anticlogging nitrogenous copolymers disclosed herein can be prepared in any convenient way. For example, such copolymers can be prepared by reacting the desired monomers in weight ratios of about 0.03 to 1 part by weight of the nitrogen-containing monomer for each part by weight of the non-nitrogenous alkyl ester monomer, in the presence of a diluent, preferably a solvent, such as toluene, benzene, ethyl acetate, or other solvents having similar chain transfer activity, at a temperature in the range of 750 C. to 0., preferably 25 C. to 150 C., in the presence of a few hundredths percent to 2 percent, preferably 0.2 to 1.0 percent, of a free radical catalyst such as benzoyl peroxide, lauroyl peroxide, or alpha, alpha-azodiisobutyroni-trile, preferably in the substantial absence of oxygen, until the rate of formation of larger polymer molecules has declined substantially, usually after about 3 to 35 hours, as determined by periodic sampling of the reaction mixture and observing the viscosity thereof.

The alkyl acrylate or alkyl alkacrylate ester monomers from which the nitrogenous anticlogging copolymers dis closed herein are prepared can be represented by the general formula: CH =CRCOOR where R is hydrogen or a lower alkyl radical such as methyl, and R is a straight or branched chain alkyl group containing 8 to 18 and preferably 12 to 18 carbon atoms, such as lauryl, Oxo-tridecyl, n-hexadecyl, or n-octadecyl.

The nitrogenous monomers from which the copolymers disclosed herein are derived are copolymerizable, unsaturated compounds containing an ethylenic linkage that is copolymerizable with the acrylate or alkacrylate monomers and a nitrogen-containing substituent group that is not copolymerizable with the acrylate or alkacrylate monomers. The nitrogen-containing substituent group can be associated with the group containing the copolymerizable ethylenic linkage through an ester linkage, a salt linkage, including quaternary ammonium salts, and addition salts, as well as the dehydrated form of the latter, that is, amides.

When the nitrogenous substituents are linked to the polymer chain through a quaternary ammonium salt linkage, the nitrogenous monomer will be a quaternary ammonium salt of acrylic acid or a lOWer acrylic acid such mers from which the herein-described copolymers can be prepared can be represented by the general formula:

RI! CH =CROOON where R is as defined above, R is an alkyl, alkenyl, or alkadienyl radical containing 12 to 18 carbon atoms, such as lauryl, myristyl, n-hexadecyl, n-octadecy, n-octadecenyl, or n-octadecadienyl, and R" and R are radicals of the same kind as R or alkyl radicals containing 1 to 4 carbon atoms such as methyl, ethyl, propyl, or butyl, or a mononuclear alkyl radical containing 7 to 23 carbon atoms such as benzyl, tolylethyl, or a polypropylated aralkyl radical such as p-tetrapropylbenzyl, and R" is an alkyl radical containing 1 to 4 carbon atoms. A specific example of a preferred anticlogging quarternary ammonium salt copolymer is the 1:9 weight ration copolymer of monomeric mixed octadecenyland octadecadienyltrimethylammonium methacrylate and monomeric lauryl methacrylate. Examples of other quarternary ammonium salt copolymers whose use is included by the invention are the 1:9 weight ratio copolymers of monomeric distearyldimethylammonium methacrylate and monomeric lauryl methacrylate and the 0.05:1, the 0.121, the 05:1, and 1:1 weight ratio copolymers of monomeric dioctadecenyldimethylammonium, octadecenyldimethylethylammonium, distearyldimethylammonium,

laurylbenzyldimethylammonium, lauryldimeth'yl(ethylben-v ZyDammQnium acrylates and methacrylates, and monomeric n-octyl, lauryl, Oxooctyl, Z-ethylhexyl, Ox-o-tri decyl, and n-hexadecyl acrylates and methacrylates. Quarternary ammonium salt copolymers of the kind disclosed herein are described and claimed as such in copending application Serial No. 862,056, filed December 28, 1959.

When the nitrogen-containing substituent group is attached to the copolymerizable ethylenic linkage-containing portion of the monomers throughv an addition salt linkage or the like, the nitrogen-containing monomers from which the anticlogging copolymers disclosed herein can be derived will be monomeric nitrogen-containing salts formed from substantially equivalent proportions of an acrylic or lower alkyl acrylic acid such as methacrylic acid and an amine having as at least one N-substituent an aliphatic hydrocarbon radical containing 8 to 18 carbon atoms. The other N-substituents can be the same as or different from the first-mentioned N-substituent, for example, the other N-substituents can bev hydrogen, aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms, or alkylol groups containing 1 to 4 carbon atoms. The preferred amine salt monomers from which the nitrogeneous addition salt-containing copolymers disclosed herein are prepared can be represented by the general formula:

where R is hydrogen or a lower alkyl radical such as; methyl,

is a secondary or tertiary amine, R is an alkyl, alkenyl, or alkadienyl radical containing 8 to 18 carbon atoms, such as lauryl, myristyl, n-hexadecyl, no-ctadecyl, n-octadecenyl, or n-octadecadienyl, and R'. is an alkylolgroup containing 1 to 4 carbon atoms such as ethylol or propylol or an aliphatic hydrocarbon radical containing l to 18 carbon atoms such as methyl, propyl, butyl, or any of those named in the description of R, and R is hydrogen or a radical of the same kind as R'.. An example of a preferred anticlogging. copolymer in which the nitrogen-containing substituent is linked to the polymer chain through an addition salt linkage is.the1:9'weight ratio copolymer of monomeric di(Oxo-octyl)ammoniurri methacrylate and monomeric lauryl methacrylate. Examples of other copolymers Whose use is included by this invention are the 3:7 Weight ratio copolymer of monomeric di(Oxo-octyl) ammonium methacrylate and monomeric lauryl methacrylate, the 1:9 weightratio copolymer of monomeric di (Oxo-octyl hydroxyethylammonium methacrylate and monomeric lauryl methacrylate, andthe 0.05:1, 01:1, 05:1, and 1:1 weight ratio copolymers of monomeric octylammonium, dioctylammonium, .trioctylammonium, laurylammonium, octadecylammonium, octadecenylammonium vacrylates and methacrylates and monomeric n-octyl, lauryl, Oxo-octyl, Z-ethylhexyl, Oxotridecyl, and n-hexadecyl acrylates and methacrylates. Amine salt copolymers of the kind disclosed herein are describedandrclaimed as such incombination withliquid hydrocarbon fuels in copending application Serial No. 33,934, filed June 6, 1960.

When the nitrogen-containing substituent of the monomers from which theanticlogging copolymers disclosed herein are derived is associated With the polymer chain through an ester linkage, the, nitrogen-containing mono mer will be a monomeric ester of acrylic acid or a lowerv alkacrylic acid such as methacrylic acid and an amine having as at least one N-substituent an alkylol group, normally containing 2 m4 carbon atoms, and as another N-substituent an aliphatic hydrocarbon radical containing 1 to 18 carbon atoms and as the third N-substituent hydrogen, an aliphatic hydrocarbon radical containing 1 to 18 carbon atoms or an alkylol radical containing 2 to 4 carbon atoms. The preferred nitrogen-containing ester monomers from which the copolymers disclosed herein are derived can be represented by the general formula:

Where R is hydrogen or a lower alkyl radical such as methyl, where n is an integer of 2' to 4, preferably 2, R isan alkyl, alkenyl, or alkadienyl radical containing 8 to 18 carbon atoms, such as Oxo-octyl, lauryl, myristyl, nhexadecyl, n-octadecyl, n-octadecenyl,. or n-octadecadienyl and R" is an aliphatic hydrocarbon radical containing 1 to 18 carbon atoms, such as methyl, ethyl or any of those comprising R. A specific example of .a preferred anticlogging copolymer in which the nitrogencontainingsubstituent is linked to the. copolymer chain through an ester linkage is the 1:9 copolymer of di(Oxo octyl)aminoethyl methacrylate and lauryl methacrylate.

Specific examples of other such copolymer are the 0.05:1, 01:1, 05:1, and 1:1 weight ratio copolymers of monomeric n-octylaminoethyl, laurylaminoethyl, octadecylaminoethyl, and octade-cenylaminoethyl acrylates and methacrylates, andmonomeric n-octyl, lauryl, Oxooctyl, 2-ethy1hexyl, Oxo-tridecyl, and n-hexadecyl acrylates and methacrylates.-

The preferred supplemental anticlogging copolymers disclosed herein-are copolymers of the above-indicated monomers in weight ratios in the range of about 0.05 to 0.75 part by weight of nitrogen-containing monomer to one part by weight of nitrogen-free ester monomer.

The average molecular weight .of the anticlogging copolymers disclosed herein will normallybe greater than about 2,000 and preferably greater than about 7,500, as determined by conventional methods. Usually the molecular weight of the copolymers will not exceed about 500,000, but the molecular weights can be greater,

provided that the molecular weight is not so great as to render the copolymer insoluble in the liquid hydrocarbon fuel distillates disclosedherein.

The oil-soluble, supplemental, anticlogging, phosphosulfurized hydrocarbon reaction products suitable for the purposes of this invention can be prepared in any convenient manner. For example, these materials can be prepared by reacting a sulfide'of phosphorus with an aliphatic hydrocarbon in relative proportions andat reaction conditions sufiicient to effect reaction'of all of the phosphorus sulfide. Thus, good results are obtainable by effecting the reaction at a temperature of about 200 to 600 F., preferably about 300 to 500 F., using a mole ratio of about 1 to 10, preferably about 2 to 5,

molecular proportions of hydrocarbonfor each molecular proportion of the phosphorus sulfide, usually in an inert atmosphere, until substantially all of the phosphorus sulfide has reacted, usually-about 2 to 10 hours. Although phosphorus pentasulfide is the preferred phosphorus sulfide, otherphosphorus sulfide such as P 8 P 8 P 8 or mixtures thereof can be used. The hydrocarbon starting 1 materials include aliphatic hydrocarbons 'such as paraf-' fins, olefins, olefin polymers, or petroleum fractions. Examples of olefins include diisobutylene, dodecene, and octadecene. Suitable olefin polymers'includethose having 1 I molecular weights of about 50 to 10,000, examples of which are polymers of ethylene, propylene, butylene,

isobutylene, and the like-or copolymers of combinations of such monoolefins. An example of a preferred phospho sulfurized hydrocarbon is the 082328 rnol ratio reaction product of P 8 and pentapropylene obtained at a reaction temperature of 220 C. over a period of about 4.5 hours. An example of another such reaction product is the reaction product of a 150 S.U.S. Mid-Continent bright stock and 10 percent by weight P 8 The polyglycerol monoesters, as well as the supplemental anticlogging agents, when they are used, can be incorporated in combustion gas turbine fuels in any suitable manner. For example, they can be added singly or in combination, either as such, or in diluted form to the fuels either promptly after distillation or after storage for an indefinite period of time. Alternatively, the addition agents disclosed herein can be added to aviation turbine fuels in admixture with other addition agents adapted to improve one or more characteristics of the fuels. For example, the addition agents disclosed herein can be added to the fuels in admixture with corrosion inhibitors, such as amine salts of oragnic esters of othophosphoric acid, antioxidants such as 2,6-di-tertiarybutyl-4-methylphenol, or 2,4-dimethyl-6-tertiary-butylphenol.

The polyglycerol monoesters disclosed herein can be employed in combustion gas turbine fuels in any proportions sufiicient to improve the thermal stability of the fuels. Normally a noticeable improvement in thermal stability, especially as regards reduction of heat transfer surface deposits, will be obtained by the use of as little as 2.5 pounds of polyglycerol monoester per thousand barrels of fuel, but it is usually desirable to employ at least five pounds per thousand barrels of fuel of the polyglycerol monoester in order to obtain a substantial improvement in thermal stability. A major improvement will ordinarily be obtained by the use of proportions in the range of about to pounds per thousand barrels of fuel. Although it is not normally necessary to exceed proportions of 20 pounds per thousand barrels of fuel, the polyglycerol monoesters can be employed in greater proportions, for example, up to 50 pounds or more per thousand barrels of fuel, in instances of fuels having unusually poor thermal stability characteristics, or in instances of relatively less effective polyglycerol monoesters. When a supplemental anticlogging agent of the kind disclosed herein is employed in the fuel, these materials can be used in the same range of proportions as the polyglycerol monoesters, and the respective materials can be employed in varying proportions with respect to one another. Normally, it is preferred to employ the polyglycerol monoesters and the supplemental anticlogging agents in approximately equal proportions, but this is not essential as other relative proportions can be employed, provided that each of the respective agents is employed in proportions of at least 2.5 pounds of agent per 1,000 barrels of fuel. By way of illustration, the polyglycerol monoesters and the supplemental anticlogging agents can be employed in weight ratios of about 1:10 to 10:1, and preferably 1:4 to 4:1.

Combustion gas turbine fuels of the type whose use is included by this invention are liquid hydrocarbon mixtures, typical of which are ordinary aviation turbine fuels, that is, jet fuels. The properties of the most common aviation turbine fuels are defined fully in the following specifications: MIL-J-5161E (Referee JP-4 Fuel), MILI-5624D (JP-4, LIP-5 Fuel), MIL-F-25656 (JP-6 Fuel), MILF- 524A (Thermally Stable Fuel), MIL-F- 25558B (RI-1 Fuel), MIL-R-25576B (RP-1 Fuel, and American Airlines Specification No. M6-4A. In general, aviation turbine fuels are characterized by the following common properties:

Thermal value, B.t.u./lb. (min.) l8,300l8,500.

8 Aniline-gravity constant 4,500, usually 5,250. Aromatics, vol. percent (max.) 5-25. Olefins, vol. percent (max.) 15.

In addition to these characteristics, it also may be noted that typical aviation turbine fuels employed for use in aviation turbine engines involving a high temperature fuel stability problem normally boil in the range of about 250 to 700 F., that is to say, these aviation turbine fuels normally boil above the gasoline range.

The ability of the materials disclosed herein to reduce formation of solid deposits in aviation turbine fuels at high service temperatures has been demonstrated by subjecting representative fuel compositions of the kind disclosed herein to the CFR Fuel Coker test procedure. This test procedure is described in detail in the Manual of ASTM Standards on Petroleum Products, ASTM D- 1660-59T. In accordance with this test method, aviation turbine fuels are subjected to flow conditions and temperature stresses similar to those in combustion gas turbine or jet aircraft engines by circulation through a simulated aircraft fuel system, maintained above 300 F., at

a rate of six pounds of fuel per hour, for a period of 300' minutes. The test apparatus comprises a fuel system containing two heated sections, on of which is a preheater section that simulates the hot fuel line sections of an aviation turbine engine as typified by the engine fuel-lubricating oil cooler. The extent of fouling of heat transfer surfaces in the preheater section by fuel degradation deposits is determined by inspection, and the extent of such fouling is used as one index of the high temperature stability of the aviation turbine fuel in the heat exchanger section of an aviation turbine engine. Preheater deposits are rated according to the following scale: 0=no visible deposits; 1=visible haze or dulling, but no visible color; 2=barely visible coloration; 3=light tan to peacock stain; 4=heavier than 3.

The second heated section comprises a filter section that simulates the nozzle area or fuel inlet area of the combustion zone of a jet engine where fuel degradation particles may be trapped. A precision, sintered stainless steel filter is employed in the filter section to trap fuel degradation particles formed during the test. The extent of the buildup of fuel degradation particles in the filter section is indicated by the pressure differential across the test filter, and this pressure differential is used as another index of the high temperature stability of the aviation turbine fuel. In carrying out the tests described the temperature of the fuel at the outlet of the preheater section is maintained at 400 F. and the filter section temperature is maintained at 500 F.

In the specific embodiments described herein the polyglycerol monoester employed was a commercial material marketed under the name Emcol 14. This material is a monooleate of a polyglycerol containing an average of four units of glycerol per molecule, together with small amounts of dioleate, free oleic acid, free glycerols, and sodium salts. The supplemental anticlogging agent employed in the test was the 1:9 weight ratio copolymer of di(Oxo-octyl)aminoethyl methacrylate and lauryl methacrylate. This material was prepared by heating a mixture of 55 grams di(Oxo-octyl)aminoethyl methacrylate, 495 grams lauryl methacrylate, 3.3 grams azodiisobutyronitrile and 1100 grams of an SAE l0/W lubricating oil, with stirring, in a stream of nitrogen for six hours at 55 C. The resulting copolymer was obtained in a viscous solution slightly lighter in color than the solvent oil. The calculated nitrogen content of 0.13 for the solution was confirmed by analysis. A similarly prepared, oil-free copolymer had an average molecular weight of about 180,- 000. The Oxo-octyl substituents of the di-(Oxo-octyl) aminoethyl methacrylate were derived from Oxo-octyl alcohol, that is, octyl alcohol prepared by the Oxo synthesis process. A typical sample of the Oxo-octyl alcohol from which the substituents were derived contained about 38 percent 4,5-dimethylhexyl alcohol, 30 percent 3,5-dimethylhexyl alcohol, percent S-methylheptyl alcohol, 19 percent 3,4-dimethylhexyl alcohol, and 3 percent 5,5- dimethylhexyl alcohol.

In the test reported below the test fuel was a commercial aviation turbine fuel having the following characteristics:

Gravity, API 43.5 Freezing point, F. 55 Sulfur, L, percent 0.055

Mercaptan sulfur, precent 0.00l

Existent gum, mg./100 ml. 0.7 Potential gum, mg./100 m1. 2.2 Aromatics, vol. percent 16.0 Olefins, vol. percent 1.0 Saturates, vol. percent 83.0 Thermal value, B.t.u./lb 18,587 Aniline-gravity constant 6,442 Distillation, kerosene:

Over point, F. 350 End point, F 572 10% evap. at, F. 386 50% evap. at, F 435 90% evap. at, F. 505

The make-up of the test samples and the results obtained in the above described tests were as set forth in the following table:

TABLE A Make-up: Percent by Volume- Aviation Turbine Fuel Stabilizer Added: Lbs/1000 Bbls.

Polyglycerol Monooleate 1:9 Wt. Ratio Copolymer Di (Oxo-octyDArninoethyl Meth- {icrylate and Lauryl Methacryate Inspections:

Thermal Stability, CFR Fuel Ooker Filter Section- Time to Reach a Pressure Drop of 10 In. Hg: Min Time to Reach a Pressure Drop of In. Hg: Min AP at 300 Min.: In. Hg Preheater Section- Maximum Preheater Deposit Rating Average Preheater Deposit Rating From a comparison of results obtained in Test Runs 1 and 2, it will be seen that incorporation of a small amount of polyglycerol monooleate in aviation turbine fuel completely eliminated preheater deposits, i.e., heat transfer surface deposits, and effected a significant reduction in filter section deposits. As indicated, the fact that the polyglycerol monooleate was effective to reduce deposits both in the preheater section as well as in the filter section is considered significant since ordinarily, inhibitors that are effective to reduce deposits in one section are ineffective to reduce deposits in the other. Comparison of the results Obtained in Test Runs 1 and 3 indicates that the supplemental anticlogging agent efiected a marked reduction in filter section deposits but failed to reduce preheater deposits. Comparison of the results obtained in Test Run 4 with those obtained in Test Runs 2 and 3 indicates that the combination of the polyglycerol monooleate and the supplemental anticlogging agent effected essentially complete reduction of both the preheater section or heat transfer surface deposits and the filter section deposits. The fact that the polymeric anticlogging agent reduces filter clogging in the presence of the polyglycerol monooleate Without diminishment of the desirable characteristics of the latter indicates a coaction between the materials, as not every material that is capable as such of reducing filter section deposits retains its TAB LE B Make-up: Percent by Volume Aviation Turbine Fuel.-. Improvement Agents Added: Lb./l000 Bbl.

Polyglycerol Monooleate Polyglycerol Monolaur e Polyglycerol Mono- Oxo-oetanoate Polyglycerol Monostearate 1:9 Wt. Ratio Copolymer of Mixed Octadecenyl and Octadeeadienyl Trimethylammonium Methacrylate and Lauryl Methacrylate- 1:9 Wt. Ratio Copolymer of Di(Oxo-octyl) Hydroxyethylammom'um Methacrylate and Lauryl Methacrylate Pentapropylene-P s Reaction Product (0.82:3.28 Mol Ratio).

It will be understood that the invention is not limited to the particular polyglycerol monoesters or supplemental anticlogging agents set forth in the preceding specific embodiments, and that other materials disclosed herein can also be employed with good results. For example, for the supplemental anticlogging agents of the preceding specific embodiments there can be substituted in proportions of, for example, 10 to 20 pounds per thousand barrels of fuel, quaternary ammonium salt copolymers such as the 1:9 weight ratio copolymers of monomeric distearyldimethylammonium methacrylate and monomeric lauryl methacrylate and the 0.05:1, the 0.1:1, the 0.5 :1, and 1:1 Weight ratio copolymers of monomeric dioctadecenyldimethylammonium, octadecenyldimethylethylammonium, distearyldimethylammonium, laurylbenzyldimethylammonium, lauryldimethyl(ethylbenzyl)ammonium acrylates and methacrylates, and monomeric n-octyl, lauryl, Oxo-octyl, 2-ethylhexyl, Oxotridecyl, and n-hexadecyl acrylates and methacrylates; addition salt copolymers such as the 3:7 weight ratio copolymer of monomeric di(Oxo-octyl)ammonium methacrylate and monomeric lauryl methacrylate, the 0.05:1, 0.1:1, 0.5: 1, and 1:1 weight ratio copolymers of monomeric octylammonium, dioctylammonium, trioctylammonium, laurylammonium, octadecylammonium, octadecenyl ammonium acrylates and met-hacrylates and monomeric n-octyl, lauryl, Oxo-octyl, 2-ethylhexyl, OXo-tridecyl, and n-hexadecyl acrylates and methacrylates; or aminoester copolymers such as the 0.05:1, 0.1:1, 0.5 :1, and 1:1 weight ratio copolymers of monomeric n-octylaminoethyl, laurylaminoethyl, octadecylaminoethyl, and octadecenylaminoethyl acrylates and methacrylates.

In addition to reducing heat transfer deposits and fuel inlet deposits in combustion gas turbine fuels, the polyglycerol monoesters disclosed herein also function to reduce electrostatic discharges by such fuels.

The combustion gas turbine fuel compositions of this invention can also contain various other addition agents adapted to improve one or more properties of the fuel. For example, the fuel compositions of this invention can contain in addition to the addition agents disclosed herein, corrosion inhibitors, freezing point depressants, antioxidants, metal deactivat-ors, combustion and/or ignition improvement agents and the like.

Many modifications and variations of the invention as herein described will suggest themselves to those skilled in the art and resort may be had to such modifications and variations without departing from the spirit and scope of the invention. Accordingly, only such limitations should be imposed as are indicated in the claims appended hereto.

We claim:

1. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel, of a combination of (A) a monoester of a fatty acid containing 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and (B) an anticlogging oil-soluble phosphosulfurized aliphatic hydrocarbon selected from the group consisting of paraflins, olefins, and olefin polymers having molecular weights in the range of about 50 to 10,000, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

2. The composition of claim 1 where said small amount comprises about 2.5 to 50 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a Weight ratio with respect to each other of about 10:1 to about 1:10.

3. The composition of claim 1 Where said small amount comprises about 10 to pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in approximately equal weight proportions.

4. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel, of a combination of (A) a monoester of a fatty acid containing 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and (B) an oil-soluble nitrogen-containing anticlogging copolymer of (i) a monomeric, copolymerizable alkyl ester of an acid selected from the group consisting of acrylic and lower alkacrylic acids whose alkyl ester substituent contains 8 to 18 carbon atoms, and (ii) a monomeric, copolymerizable unsaturated compound containing an ethylenic linkage as the sole functional group that is copolymerizable with the aforesaid monomeric alkyl ester and a nitrogen-containing substituent group, said monomeric components being present, respectively, in the copolymer in a weight ratio of about 0.03 to 1:1, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

5. The composition of claim 4 where said small amount comprises about 2.5 to 50 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a weight ratio with respect to each other of about 10:1 to about 1:10.

6. The composition of claim 4 where said small amount comprises about 10 to 20 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in approximately equal weight proportions.

7. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel of a combination of (A) a monoester of a fatty acid having 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and (B) an oil-soluble nitrogen-containing anticlogging copolymer of (i) a monomeric, copolymerizable alkyl ester of an acid selected from the group consisting of acrylic and lower alkacrylic acids whose alkyl ester substituent contains 8 to 18 carbon atoms, and (ii) a monomeric, copolymerizable ester of an acid selected from the aforesaid group and' an amine having as at least one N-' substituent an alkylol group containing 2 to 4 carbon atoms and as another N-substituent an aliphatic hydrocarbon radical containing 1 to 18 carbon atoms and as another N-substituent a member selected from the group consisting of hydrogen, aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms and alkylol radicals containing 2 to 4 carbon atoms, said monomeric components being present, respectively, in the copolymer in a weight ratio of about 0.05:1 to 0.75:1, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

8. The composition of claim 7 where said small amount comprises about 2.5 to 50 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a Weight ratio with respect to each other of about 10:1 to about 1:10.

9. The composition of claim 7 where said small amount comprises about 10 to 20 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in approximately equal Weight proportions.

10. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel, of a combination of (A) a monoester of oleic acid and a polyglycerol containing an average of about four -CH CHOHCH O units per molecule, and (B) an approximately 1:9 weight ratio copolymer of (i) di(Oxo-octyl) aminoethyl methacrylate and (ii) lauryl methacrylate, said small amount comprising about 5 to 20 pounds of each member of said combination per thousand barrels of fuel, said members being present in the composition in a Weight ratio with respect to each other of about 4:1 to 1:4.

11. A process for reducing formation of carbonaceous deposits by thermally unstable hydrocarbon oils on hot, heat transfer surfaces, comprising incorporating in a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel that normally tends to form deposits upon hot, heat transfer surfaces contacted thereby, prior to contact with said heat transfer surfaces, a small amount, sufficient to reduce deposit formation of a monoester of a fatty acid containing 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and then heating the fuel by contact with a heat transfer surface at a temperature in excess of 300 F.

12. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel, of a combination of (A) a monoester of a fatty acid containing 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and (B) a member selected from the group consisting of (1) an anticlogging, oil-soluble phosphosulfurized aliphatic hydrocarbon selected from the group consisting of parafiins, olefins, and olefin polymers having molecular weights in the range of about 50 to 10,000 and (2) an oil-soluble, nitrogen-containing anticlogging copolymer of (i) a monomeric, copolymerizable alkyl ester of an acid selected from the group consisting of acrylic and lower alkacrylic acids whose alkyl ester substituent contains 8 to 18 carbon atoms, and (ii) a monomeric copolymerizable unsaturated compound containing an ethylenic linkage as the sole functional group that is copolymerizable with the aforesaid monomeric alkyl ester and having a nitrogen-containing substituent group, said monomeric components being present, respectively, in the copolymer in a weight ratio of about 0.03 to 1:1, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

13. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sutficient to improve the thermal stability of said fuel, of a combination of (A) a monoester of a fatty acid containing 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and (B) an oil-soluble nitrogen-containing anticlogging copolymer of (i) a monomeric copolymerizable alkyl ester of an acid selected from the group consisting of acrylic and lower alkacrylic acids Whose alkyl ester substituent contains 8 to 18 carbon atoms, and (ii) a monomeric, copolymerizable unsaturated compound containing an ethylenic linkage as the sole functional group that is copolymerizable with the aforesaid monomeric alkyl ester, and having a nitrogen-containing substituent associated with the group containing the copolymerizable ethylenic linkage through a linkage selected from the group consisting of ester, amine addition salt, amido and quaternary ammonium linkages, said monomeric components being present, respectively, in the copolymer in a weight ratio of about 0.03:1 to 1:1, said copolymer having an average molecular weight in the range of about 2,000 to about 500,000, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

14. The composition of claim 13 where said small amount comprises about 25 to 50 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a weight ratio with respect to each other of about 10:1 to about 1:10.

15. The composition of claim 13 where said small amount comprises about 10 to 20 pounds of each member of said combination per thousand barrels of said fuel, and the members are present in the composition in approximately equal weight proportions.

16. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufiicient to improve the thermal stability of said fuel, of a combination of (A) a monoester of a fatty acid containing 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and (B) a member selected from the group consisting of (1) an anticlogging oil-soluble phosphosulfurized aliphatic hydrocarbon selected from the group consisting of paraffins, olefins, petroleum fractions and olefin polymers having molecular weights in the range of about 50 to 10,000, and (2) an oil-soluble nitrogen-containing anticlogging copolymer of (i) a monomeric, copolymerizable alkyl ester of an acid selected from the group consisting of acrylic and lower alkacrylic acids whose alkyl ester substituent contains 8 to 18 carbon atoms and (ii) a monomeric, copolymerizable unsaturated compound containing an ethylenic linkage as the sole functional group that is copolymerizable with the aforesaid monomeric alkyl ester, and having a nitrogen-containing substituent associated with the group containing the copolymerizable ethylenic linkage through a linkage selected from the group consisting of ester, amine addition salt, amido and quaternary ammonium linkages, said monomeric components being present, respectively, in the copolymer in a weight ratio of about 0.03:1 to 1:1, said copolymer having an average molecular weight of about 2,000 to about 500,000, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

17. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel of a combination of (A) a monoester of a fatty acid having 8 to 18 carbon atoms per molecule and a polyglycerol having an average molecular weight of about 166 to 462, and (B) an oil-soluble nitrogen-containing anticlogging copoly* mer of (i) a monomeric, copolymerizable alkyl ester of an acid selected from the group consisting of acrylic and lower alkacrylic acids whose alkyl ester substituent contains 8 to 18 carbon atoms, and (ii) a monomeric, co polymerizable ester of an acid selected from the aforesaid group and an amine having as at least one N-substituent an alkylol group containing 2 to 4 carbon atoms and as another N-substituent an aliphatic hydrocarbon radical containing 1 to 18 carbon atoms and as another N-substituent a member selected from the group consisting of hydrogen, aliphatic hydrocarbon radicals containing 1 to 18 carbon atoms and alkylol radicals containing 2 to 4 carbon atoms, said monomeric components being present, respectively, in the copolymer in a Weight ratio of about 0.05:1 to 0.75:1, said copolymer having an average molecular weight in the range of about 2,000 to about 500,- 000, said small amount comprising at least about 2.5 pounds of each member of said combination per thousand barrels of fuel.

18. The composition of claim 17 where said small amount comprises about 2.5 to 50 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in a weight ratio with respect to each other of about 10:1 to about 1:10.

19. The composition of claim 17 where said small amount comprises about 10 to 20 pounds of each member of said combination per thousand barrels of fuel, and the members are present in the composition in approximately equal weight proportions.

20. A fuel composition comprising a major amount of a normally thermally unstable liquid hydrocarbon combustion gas turbine fuel and a small amount, sufficient to improve the thermal stability of said fuel, of a combination of (A) a monoester of oleic acid and a polyglycerol containing an average of about four units per molecule, and (B) an approximately 1:9 weight ratio copolymer of (i) di(Oxooctyl)aminoethyl methacrylate and (ii) lauryl methacrylate, said copolymer having an average molecular weight in the range of about 2,000 to about 500,000, said small amount comprising about 5 to 20 pounds of each member of said combination per thousand barrels of fuel, said members being present in the composition in a weight ratio with respect to each other of about 4:1 to 1:4.

References Cited by the Examiner UNITED STATES PATENTS 2,221,674 11/1940 Ellis 260--410.6 2,548,347 4/ 1951 Caron et al. 44-66 2,737,452 3/1956 Catlin et al. 4462 2,768,999 10/1956 Hill 252-327 X 2,805,925 9/ 1957 Biswell 44-62 FOREIGN PATENTS 24,109/35 3/1936 Australia.

452,138 8/1936 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

LEON D. ROSDOL, Examiner. 

12. A FUEL COMPOSITION COMPRISING A MAJOR AMOUNT OF A NORMALLY THERMALLY UNSTABLE LIQUID HYDROCARBON COMBUSTION GAS TURBINE FUEL AND A SMALL AMOUNT, SUFFICIENT TO IMPROVE THE THERMAL STABILITY OF SAID FUEL, OF A COMBINATION OF (A) A MONOESTER OF A FATTY ACID CONTAINING 8 TO 18 CARBON ATOMS PER MOLECULAR WEIGHT OF ABOUT 166 TO 462, AND (B) A MEMBER SELECTED FROM THE GROUP CONSISTING OF (1) AN ANTICLOGGING, OIL-SOLUBLE PHOSPHOSULFURIZED ALIPHATIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF PARAFFINS, OLEFINS, AND OLEFIN POLYMERS HAVING MOLECULAR WEIGHTS IN THE RANGE OF ABOUT 50 TO 10,000 AND (2) AN OIL-SOLUBLE, NITROGEN-CONTAINING ANTICLOGGING COPOLYMER OF (I) A MONOMERIC, COPOLYMERIZABLE ALKYL ESTER OF AN ACID SELECTED FROM THE GROUP CONSISTING OF ARCYLIC AND LOWER ALKACYLIC ACIDS WHOSE ALKYL ESTER SUBSTITUENT CONTAINS 8 TO 18 CARBON ATOMS, AND (II) A MONOMERIC COPOLYMERIZABLE UNSATURATED COMPOUND CONTAINING AN ETHYLENIC LINKAGE AS THE SOLE FUNCTIONAL GROUP THAT IS COPOLYMERIZABLE WITH THE AFORESAID MONOMERIX ALKYL ESTER AND HAVING A NITROGEN-CONTAINING SUBSTITUENT GROUP, SAID MONOMERIC COMPONENTS BEING PRESENT, RESPECTIVELY, IN THE COPOLYMER IN A WEIGHT RATIO OF ABOUT 0.03 TO 1:1, SAID SMALL AMOUNT COMPRISING AT LEAST ABOUT 2.5 POUNDS OF EACH MEMBER OF SAID COMBINATION PER THOUSAND BARRELS OF FUEL. 